Definition
Bounce rate is the percentage of sent emails that couldn't be delivered and were returned to you.
bounce rate = bounced emails ÷ emails sent × 100
Hard vs soft bounces
- Hard bounce — permanent: the address or domain doesn't exist. Remove it immediately.
- Soft bounce — temporary: full mailbox, server busy, message too large. Retry later; remove if it keeps happening.
Why it matters
Inbox providers use bounces as a signal of list quality. Many hard bounces suggest an old, bought or guessed list — patterns associated with spam — and can push your future emails to spam.
Common causes
- old lists where people left the company
- guessed email addresses
- typos in addresses
- domains that expired
Keeping it low
- build fresh lists from live sources
- prefer emails published by the business
- verify before large sends (email verification)
- remove hard bounces immediately
- warm up new domains and keep volume modest
If your bounce rate rises suddenly, pause sending and check the list before continuing.
Example
You send 1,000 emails and 40 come back: 30 hard bounces (addresses that don't exist) and 10 soft bounces (full mailboxes). Your bounce rate is 4%. Removing the 30 hard bounces and verifying the next list brings it down.
Key takeaways
- Hard bounces are permanent; remove them right away.
- High bounce rates hurt deliverability.
- Fresh lists and verification keep bounces low.